1. Field of the Invention
This invention relates to a multi-layer optically clear laminate suited for attachment to window glass to provide a glazing element which has reduced spall and lacerative consequences on impact fracture of the window glass and to glazing elements made with the same.
2. Description of Related Art
The invention of laminated glass windshields for use in motor vehicles has substantially reduced injuries caused by occupant-windshield impacts resulting from automobile accidents. Such laminated windshields are made by laminating under heat and pressure two glass plates with an interlayer of a tough, transparent, extensible, material such as polyvinyl butyral (PVB). While such a laminated windshield provides some degree of protection for motor vehicle occupants, it is still generally conventional to utilize unlaminated glazing elements for fabricating the other windows of automobiles. While such windows are typically tempered so that on impact they fracture in small irregular pieces without producing knife-like shards, they still provide a hazard to the occupants of a motor vehicle. The impact fracture of such automotive glazing typically produces what is called “spall.” Spall is the shower of glass splinters that typically results from the impact fracturing of automotive glazing. Such glass splinters could have a lacerative effect on the occupants of the motor vehicle and on any air bag that may have been inflated as a result of the automobile accident.
There is a growing trend to replace tempered glass with laminated glass (glass/PVB/glass) as motor vehicle sidelights to provide additional safety. However, when laminated sidelights are broken, they typically leave sharp glass shards attached to the PVB interlayer which can cause severe laceration to the occupants of the vehicle. Thus, a need exists for an acceptable anti-spall, anti-lacerative (ASL) film that will provide a barrier between the broken glass shards and the vehicle occupant to minimize the opportunity for laceration.
Furthermore, in the case of automobiles, there is a practice called “smash and grab” utilized by thieves intending to steal the contents of automobiles which provides immediate access on impact of tempered glass automotive windows. A need also exists for a stronger window film which will sustain such fractures without rupture.
The impact fracture problem also exists in the case of architectural glazing where tempered or annealed glass panels are employed for windows and doorways. Impact fracturing of such glass panels may cause spall which would be a hazard to anyone in the immediate vicinity of the fractured panel.
The use of laminates to reinforce glazing is well known. For example, U.S. Pat. No. 4,072,779 (Knox, et al.) is directed to a laminate which includes a frangible, transparent, asymmetrically oriented polyethylene terephthalate film laminated to a polyvinyl butyral sheet and coated on the opposite surface with an abrasion-resistant coating. This laminate is adhered to a glass panel by sandwiching it between the glass panel and a second glass panel under heat and pressure and discarding the nonadhered glass panel once the lamination is completed. It is believed that the laminate is commercially available from the E.I. DuPont de Nemours and Company, Circleville, Ohio under one or more of the tradenames SENTRY GLASS™ and BE-1028 SPALLSHIELD™ sheeting.
U.S. Pat. No. 4,112,171 (Motter, et al.) discloses a laminate which is said to provide anti-lacerative and anti-spall properties. U.S. Pat. No. 4,945,002 (Tanuma, et al.) discloses an impact-resisting anti-lacerative window glass unit comprised of two exterior plate-like members made of a transparent organic first polymer and a transparent organic second polymer or glass plate to provide a multilayered structure wherein the intermediate layer could be polyethylene terephthalate.
U.S. Pat. No. 4,683,172 (LeGrand, et al.) discloses a safety or impact resistant laminate comprised of at least two laminae with an interlayer imposed therebetween bonded together by contact or pressure sensitive adhesive. The interlayer is said to be what is know in the art as an adhesive interlayer such as polyvinyl butyral.
While there is a multitude of patents disclosing various combinations of providing anti-spall and anti-lacerative laminates, none has produced a commercially acceptable product which is easy to apply under ambient conditions to provide a commercially acceptable result. Many of the products are relatively thick and thus difficult to apply, requiring heat, pressure and/or expensive application equipment. Others may not withstand the rigors of changing seasons where during winter an automotive interior may be cooled to frigid temperatures and in the summer may be heated to a sweltering temperature. Others have inherent problems because of incompatibility of some of the materials forming the laminate. Some materials will cause undesirable optical patterns when attached to automotive glazing material. Still others are frangible and do not provide the necessary strength to sustain a fracture producing impact of the glass panel while still providing the anti-spall and anti-lacerative effect.